segmentation

It expresses one of the prime characteristics of this class of animals, namely, that of segmentation.

This membrane rests with its extreme edge on the white yolk, its central portion covering in the segmentation cavity.

It is formed coincidently with the latter out of apparently similar segmentation cells.

In the chick the mesoblast cells are formed directly from the ultimate products of segmentation.

At this time also the greatest number of formative cells are to be found at the bottom of the now large segmentation cavity.